This invention relates to a method for detecting targets and determining their distance by using an HPRF (High Pulse Repetion Frequency) radar system.
Radar systems are used in flying, floating or ground-supported platforms. Various waveforms are used during operation to take into account the various use scenarios and requirements of the particular radar system. One such waveform is high PRF.
An important use scenario of HPRF radar is, for example, self defense for ships in coastal regions where the discovery of very rapid low-flying rockets, which are difficult to detect, highly maneuverable and appear suddenly and without warning, is essential to survival. Such threats in coastal regions are represented by so-called anti-ship cruise missiles (ASCM) which have a reduced detectability (radar cross section approx. 0.01 m2) and thus greatly shorten the response time to combat the missile.
As a consequence, this new situation demands special sensors that are capable of detecting these targets even in a great deal of clutter, e.g., reflection from cliffs or fiords. In addition, the sensors, i.e., radar, should be able to differentiate these small rockets from land and sea traffic, windmills and birds, whose backscatter cross section is of the same order of magnitude as that of the small rockets, and to do so at the time of detection.
In situations with a large number of targets, radar is necessary because it can detect a great many small targets and on the other hand can differentiate threatening from non-threatening among these many targets. In addition, the response time until recognition of a small target as a threat is also greatly reduced so that there is enough time to take defensive measures.
The object of the present invention is therefore to provide a method which eliminate the disadvantages of the known radar methods.
This invention includes the following method steps in which:
successive bursts are transmitted with a preselectable time lag, where the time lag corresponds to a preselectable number E of transmission pulses,
the echo signals are received in the reception time windows between the individual transmission pulses and in the E reception time windows between successive bursts,
a data record of Z+E detected signals is generated, where Z denotes the number of transmission pulses within a burst, and each detected signal is a superpositioning of echo signals from different unique distance ranges, where each distance range includes a number A of distance lines, each with Z+E distance cells,
for detection of a target, the spectrum of a Z+E-point fast Fourier transform is calculated for each distance line, a decision being made regarding a target in a distance line when the signal amplitude is greater than a preselected threshold value,
to determine the exact distance of a target, spectra of Z-point fast Fourier transforms are calculated for the distance lines such that a Z-point FFT window is shifted incrementally over the Z+E distance cells of a distance line,
the distance cell having the greatest target signal amplitude is determined by comparing the individual spectra.